Lakeroadster's Finless Rocket Utilizing Gas-Dynamic-Stabilization

[lakeroadster]

Redesigned the cartridge for the silo launcher, and painted the spin tabs red.

 

[Daddyisabar]

Alt schule Rot, weise und Swartz ist wounderbar! Mit clappen. Nicht stompen. Gut lucken on pressen ein butten.

 

[lakeroadster]

Did a swing test on THUNK! this morning. It flies backwards.... every time.... consistently. Which makes sense since OR shows negative stability. If all goes according to plan the motor exhaust will induce the GDS stability during the actual launch.

I'm also re-thinking the first launch of this rocket. I think it would be better to try launching the rocket with the bottom of the silo open and the GDS portion exposed below the silo.

If this works, and the rocket is stable, we'll get a couple launches on the flight log and then try the closed silo piston launch approach.

I just don't want to hit the launch button, hear the motor burning, and nothing happens except the rocket burns up inside it's PVC sarcophagus.

So, I mocked up the 2" silo on my launch horse. Easy assembly at the field by simply attaching the pvc to the 5/16" launch rod using a couple Quick Clamps.

See any reason this tube launch set-up won't work?

 

[lakeroadster]

Clear Coat...

As a side note I used a Sharpie to write THUNK on the rocket. I'd read here that clearcoat over a Sharpie will lead to the Sharpie text bleeding / running. That didn't happen. I made sure to put a light coat of clear over the area of the rocket with the text first, then waited an hour and applied a 2nd coat.

 

[Daddyisabar]

Clear Coat...

As a side note I used a Sharpie to write THUNK on the rocket. I'd read here that clearcoat over a Sharpie will lead to the Sharpie text bleeding / running. That didn't happen. I made sure to put a light coat of clear over the area of the rocket with the text first, then waited an hour and applied a 2nd coat.

View attachment 528687

The patience of a Jedi. Keeping your mind on where you are at, what you are doing.

 

[BigMacDaddy]

What is the purpose of the whiskers on the top of the tube?

 

[lakeroadster]

What is the purpose of the whiskers on the top of the tube?

When I do a piston launch (seal the bottom of the silo and install the rear closure in the rocket) the cat whiskers strip the rear closure out of the rocket. I'm not going to do that for the maiden launch though.

 

[lakeroadster]

And upon further reflection....

For review: This rocket started out to mimic the IKAROS marine flare. Looking at it the flare is unused and intact during the entire flight. That's a lot of nose weight.

Therefore, I decided to add nose weight to THUNK. Why? I'm wanting to verify that the GDS works. So, if I make the rocket just slightly unstable, and the GDS works, and can always start removing some nose weight.

The nose weight takes the stability from -1.45 caliber, to -0.25 caliber

 

[lakeroadster]

@lakeroadster's Thunk gave me an inspiration. I'm making a similar rocket. It's a 29mm motor tube. 4 fins top and bottom. 24" long. I have a 3" x 48" mortar tube that I fly a rocket that looks like a 60mm mortar bomb out of. I have sized the fins to fit inside the tube. I have the fins on and the nose cone has a load of BB's and epoxy. If needed I'll add more weight below the nose cone. Now I need to pick a motor. G80-13 maybe. Probably not a good choice for a first flight. I'll pick a motor that will keep the rocket in sight. I think that by the time the rocket clears the tube it will be spinning like a top. That last line made me think, when was the last time I played with a top. Easy answer. A long time ago. Late 60's I think. The mind is amazing. I can picture the top in my mind. It was wood with a metal tip. Red I think. But I can't remember what I did last week. When was the last time you all played with a top? I know. I'm rambling.

Sounds like a fun project.

Open Rocket shows a roll rate of 23 rev/sec when THUNK! clears the silo. Maximum rev's is at apogee, and is a bit over 45 rev/sec. That's a lot of RPM's... 45 rev/sec = 2700 RPM. At ejection the roll rate is down to 3.7 rev/sec. = 222 RPM. I'm wondering just what is going to happen when the chute deploys? I have swivels and a long Kevlar chord and an elastic chord too.

Weather permitting, I hope to get THUNK! launched this week.

 

[lakeroadster]

Built the 2" threaded Piston Launch Cartridge for my launch silo.

Only revision is I flipped the bolt so its threads aren't being impacted by the motor exhaust.

 

[teepot]

Sounds like a fun project.

Open Rocket shows a roll rate of 23 rev/sec when THUNK! clears the silo. Maximum rev's is at apogee, and is a bit over 45 rev/sec. That's a lot of RPM's... 45 rev/sec = 2700 RPM. At ejection the roll rate is down to 3.7 rev/sec. = 222 RPM. I'm wondering just what is going to happen when the chute deploys? I have swivels and a long Kevlar chord and an elastic chord too.

Weather permitting, I hope to get THUNK! launched this week.

View attachment 529410

Wow. That's fast. I had no idea it would spin that fast. That's as fast as a bullet. I'm going to paint the fins in a white and black roll pattern. It will just be a blur.

 

[lakeroadster]

Wow. That's fast. I had no idea it would spin that fast. That's as fast as a bullet. I'm going to paint the fins in a white and black roll pattern. It will just be a blur.

FWIW... rpms vary depending on rifling and muzzle velocity but a bullet spins at over 100,000 rpm's.

I doubt that these rockets will actually spin 2700 rpm. They aren't balanced, so that will limit the rev's. With any luck I'll get some video / photos of THUNK! exiting the silo so we can get a visual.

Hoping to launch Tuesday or Wednesday.

 

[teepot]

FWIW... rpms vary depending on rifling and muzzle velocity but a bullet spins at over 100,000 rpm's.

I doubt that these rockets will actually spin 2700 rpm. They aren't balanced, so that will limit the rev's. With any luck I'll get some video / photos of THUNK! exiting the silo so we can get a visual.

Hoping to launch Tuesday or Wednesday.

I got seconds and minutes mixed up. I thought it was 2700 rev. per sec. My bad.

 

[lakeroadster]

Launch Report

We launched THUNK! today. It was an exciting launch. The rocket flew stable and was recovered undamaged.

A D12-5 motor was used, and a 12" nylon parachute.

The Gas Dynamic Stabilization stops when the motor thrust stops. To ensure the rocket remains stable throughout the flight the rocket is designed to spin by utilizing (6) small, canted spin tabs.

Under thrust the rocket was very stable but once the thrust stopped you could see corkscrews in the smoke trail, which I assume is due to the rocket spinning and the fact that the rocket is not dynamically balanced. Items like the metal motor retention clip would create an imbalance.

The rocket did weathercock which we found a bit surprising since it does not have fins.

The Open Rocket simulation shows parachute deployment around a second after apogee. And this is what happened during the actual flight.

The interior of the GDS portion of the rocket wasn't burned as bad as I expected, but there was considerable discoloration at the top of the body tube near at the nose cone location.

 

[neil_w]

Congrats!

 

[jim_kc]

Nice flight! That is surprising about the weathercocking.

 

[BigMacDaddy]

Nice flight (My D-powered rockets never get up that high). Surprised no "thunk" though

 

[lakeroadster]

Nice flight (My D-powered rockets never get up that high). Surprised no "thunk" though

Open Rocket showed a 511 ft. apogee. It seems like it bettered that?

If I end up doing a piston launch... then it ought a thunk! That or just sit there and burn up inside the pvc...

 

[lakeroadster]

Should I launch Thunk! again, but with the GDS ports blocked with some aluminized tape, just to see if the stability was truly from GDS, and not from it spinning?

What do you think folks? Is it worth risking Thunk! as a possible sacrifice to The Rocket Stability Gods?

 

[BigMacDaddy]

Should I launch Thunk! again, but with the GDS ports blocked with some aluminized tape, just to see if the stability was truly from GDS, and not from it spinning?

What do you think folks? Is it worth risking Thunk! as a possible sacrifice to The Rocket Stability Gods?

What might be ideal would be adjustable ports so you can launch several times as you slowly close the ports to see if there is an optimal gap as well as a threshold where GDS no longer functions

 

[BABAR]

Had I spoken up I would be dining on crow now. Really had doubts this would work, another of this times I am happy to be wrong. As usual, your building and imaginative talents are rewarded by successful flights.

!Enhorabuena mucho! (!Mi espanol esta muy mal!)